Stockholders' Equity (Deficit) - Common Stock for Future Issuance (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Common stock shares reserved for future issuance (in shares)	13,177,766	12,371,042
2016 Stock Plan
Class of Stock [Line Items]
Common stock shares reserved for future issuance (in shares)	388,463	699,376
Warrants to Purchase Common Stock
Class of Stock [Line Items]
Common stock shares reserved for future issuance (in shares)	10,000,000	10,000,000
Outstanding stock options
Class of Stock [Line Items]
Common stock shares reserved for future issuance (in shares)	1,789,303	1,671,666
Stock Appreciation Rights (SARs)
Class of Stock [Line Items]
Common stock shares reserved for future issuance (in shares)	1,000,000	0